Vestaxx window heating - experiences?

- Andreas, since you are also in talks with many people (Fraunhofer etc.), I would suggest having a master's thesis done somewhere. It's little effort (except for the creator ;)) and you have a good basis for discussion.

Good point - we are already working on that ;) But we also want to have the full cost accounting we created reviewed by an independent institute.

Good point - we are already working on that ;) But we also want to have the full cost accounting we created checked by an independent institute.

Addendum -> Currently, a comprehensive study is being conducted by ISFH Hameln in cooperation with the Jülich Research Center. Houses built almost identically with different heating technologies are being examined and extensively measured. However, the results will probably not be available until next year. Then it will be even easier to argue, for example.

Let's assume a heat pump including underfloor heating costs €25,000 more than a window heating system including [BWWP], resulting in a payback period of not even 17 years.

Are the €25k already well-founded? It even seems quite a lot to me as a difference, but I don't know the exact details either.
However, one must also consider in this cost comparison: The heating system might eventually wear out and need to be replaced, but the underfloor heating usually remains intact. That means the costs for the underfloor heating should essentially be considered separately again.

I'll throw this basis into the room:

150m² with 40kWh/m²a -> 6000kWh/a heating energy demand
10kWp photovoltaic + 5kWh storage -> ~15kWh/day in Nov, Dec, Jan, Feb. With 10kWh for household electricity including hot water, 5kWh/day remain for heating
Electricity purchase price 35ct/kWh
Price of lost feed-in tariff: 8.2ct/kWh

Direct heating:
4 [months] * 30 [days] * 5 [kWh/day] = 600 [kWh] from photovoltaic electricity
Remaining 5400kWh as purchase
Totals 5400*35+600*8.2=1939.2€

Heat pump:
Electricity demand: 6000/4=1500
Remaining 900 for purchase
Totals 900*35+600*8.2=364.5€

So you save over 1500€ per year in heating costs.

Assuming a heat pump including underfloor heating costs 25000€ more than a window heater including BWWP, the payback period results in not even 17 years.

First of all, thanks RotorMotor for taking the trouble and presenting an example calculation.

I’m eager to answer this immediately, but right now I don’t have time for it. I invest a lot of time here and (mostly) enjoy dealing with your arguments, but I also have to run the company on the side ;) On Monday I’ll be sitting on the train for hours again and the answer will come by then at the latest.

Are the 25k already substantiated? Seems like quite a lot to me as a difference, but I’m not exactly sure. One has to consider in the cost comparison, though: The heating system may eventually wear out and need to be replaced, but the underfloor heating usually remains intact. That means the costs for the underfloor heating should basically be considered separately.

A quick short note on that: Every heating system will eventually fail and need to be replaced. Usually only the generator (heat pump) and not the distributor (underfloor heating). Still, problems do arise eventually and then it gets really, really expensive. And looking at it compared to the argument: What if you (Vestaxx) are no longer around in 20 years? Where would one get a replacement glass then?

Quick note on that:
Every heating system eventually wears out and has to be replaced. Usually only the generator (heat pump) and not the distributor (underfloor heating). Still, problems will arise sooner or later with it as well, and then it gets really, really expensive.

When we built the first time, we were worried about that too, but meanwhile (after I also observed the installation back then) – what is supposed to happen to the underfloor heating that is completely embedded in the screed? I mean the pipes? If a pipe really breaks in the screed (why should it), usually the building insurance covers something like that?
I primarily see the risk with the pump or so, which is located above the floor and can be replaced.

And looking at it compared to the argument: What if you (Vestaxx) are no longer around in 20 years? Where will one get a replacement glass then?

I would be less worried about single providers – if the window heating system catches on, presumably more providers will have established themselves in 20 years.
The decision in favor of window heating rather carries the risk that switching later to a system with underfloor heating is not possible without considerable costs. Therefore, it may be more interesting for renovations than for new builds. Existing buildings often face the problem of not having underfloor heating. And installing it afterwards is expensive.